Pre-and post-heating bar-concrete bond behavior of CFRP-wrapped concrete containing polymeric aggregates and steel fibers: Experimental and theoretical study

Abstract

The present research attempted to explore the impact of steel fibers and carbon fiber-reinforced polymer (CFRP) sheets on the pre-and post-heating bond behavior of steel bars in high-strength concrete incorporating waste polyethylene terephthalate (WPET) by conducting the pullout and beam tests and in both pullout and splitting failure modes. To achieve this aim, one hundred and forty-four cubes and forty-eight prisms were cast for the pullout and beam tests, respectively. The variable parameters included the replacement ratio of the fine aggregates with waste polyethylene terephthalate (WPET) particles (0 % and 10 % by volume), steel-fiber content (0 % and 1 % by volume), bar diameter (12-and 16-mm), target temperature (25, 200, and 600 °C), and confinement level (no confinement or CFRP wrapping applied after the thermal regime). Bond strength, bond stress-slip behavior between rebar and concrete, failure mode, and rebar debonding energy were among the parameters investigated after cooling. The results showed that in contrast with the positive effect of CFRP sheets on debonding energy, steel fibers have a positive effect on debonding energy only at 600 °C. Steel fibers did not offset the negative effect of polymeric aggregate, negatively changed the pullout mode to a mixed pullout/splitting failure at 200 °C, and tended to favor splitting failure mode to mixed mode at 600 °C. Moreover, steel fibers negatively affected the bond strength of pullout specimens in both confined and unconfined conditions, especially at 25 and 200 °C, and were less effective than CFRP sheets in avoiding splitting. Small-diameter bars reduced the negative effect of steel fibers on the bond, while polymeric aggregate tended to enhance the bond strength differences between large- and small-diameter bars. The effect of increasing the bar diameter on the effectiveness of CFRP sheets on the bond strength was not clear, but as a general trend, the effectiveness increased with the increase of the bar diameter. A predictive model based on the experimental results of this study and other studies was proposed as well to introduce the positive effect of the CFRP confinement and the dubious effect of steel fibers and polymeric aggregate on bond strength.